Curtain wall systems are exterior wall systems on multi-story buildings that are made of appropriate cladding materials (e.g., glass, aluminum, stone, concrete, etc.) and which carry no superimposed vertical (gravity) loads. Hence, the term “curtain” implies that a curtain wall system is essentially “hung like a curtain” from the primary structural frame of the building. A curtain wall system does not, by itself, help a building stand erect.
Although curtain wall systems are normally considered to be “non-structural” parts of a building, such terminology is misleading because curtain walls must have the ability to withstand structural loads imposed by natural phenomena such as earthquakes and severe windstorms. In this context, the term “curtain wall” is a misnomer because non-structural parts of a building can be subjected to structural loads. This invention focuses on a curtain wall system that is highly resistant to the potentially damaging effects of earthquake-induced movements of building frames.
Many curtain wall systems are constructed with glass window elements glazed within an assemblage of aluminum framing members. Architectural glass, due to its brittle nature, is inherently vulnerable to curtain wall movements during earthquakes. Research studies have been conducted to investigate the seismic performance of various types of architectural glass elements held within various aluminum curtain wall framing systems using various glazing systems. Among the findings of these studies were the following: (1) architectural glass is vulnerable to damage and fallout under simulated earthquake conditions; (2) horizontal, in-plane racking movements of a curtain wall frame constitute the primary cause of glass damage and glass fallout under simulated earthquake conditions; (3) different types of architectural glass exhibit different degrees of resistance to glass fallout under simulated seismic conditions; and (4) flexural stiffness of aluminum framing members has an influence on the susceptibility of architectural glass to seismic damage (i.e., under simulated seismic conditions, stiffer curtain wall frames are associated with more glass damage and glass fallout than are more flexible frames).
Architectural glass is not the only type of curtain wall element that is vulnerable to fracture and fallout under earthquake conditions. Curtain wall systems comprised of any rigid, brittle elements such as stone panels, cementitious panels, etc. are also potentially vulnerable to the damaging effects of earthquake-induced building motions.
The primary factors causing earthquake-induced damage of conventional curtain wall systems are: (1) movements of the building's primary structural frame in response to earthquake ground movements; and (2) the fact that vertical framing members (mullions) in conventional curtain wall systems are connected structurally to more than one floor of the primary structural frame.
The present invention is directed to solving one or more of the problems discussed above in a novel and simple manner.